1. Field of the Invention
The present invention relates to a length measuring probe.
2. Description of the Related Art
Such length measuring probes are employed in manufacturing technology for measuring workpieces. For example, the thickness, width, length, depth, as well as the inner or outer diameters can be determined.
A length measuring probe is described in U.S. Pat. No. 5,072,174, the entire contents of which are incorporated herein by reference. A probe pin is seated in a base body by a guide element of a ball bearing guide, so that it is displaceable in the longitudinal direction. The contact pressure required for scanning a workpiece to be measured by touch is generated by a helical spring, whose one end is fixed on the probe pin and the other end on the base body.
The length of the helical spring must correspond at least to the lift of the probe pin, however, long helical springs have a tendency to kink laterally. The greater the desired lift of the probe pin, the longer the ball bearing guide must be embodied in order to be able to absorb the lateral forces introduced by the probe pin in the course of touch scanning because of the lever effect. Therefore length measuring probes with a relatively large measuring range—i.e. lift of the probe pin—are constructed to be relatively long.
For shortening the structural length of a length measuring probe, two ball bearing guides are provided in accordance with U.S. Pat. No. 4,347,492, the entire contents of which are incorporated herein by reference, which are spaced apart from each other. A detection device for detecting the position of the probe pin is arranged between these two ball bearing guides. The helical spring is located in a bore in the probe pin, which requires a relatively thick probe pin. In the case where a large lift of the probe pin is required and a long helical spring is used, the problem of kinking also occurs here, which causes friction between the helical spring and the probe pin.